Dialog to allow a user to change the background color of a given document.
This is only in DEBUG for the moment, until I fix it up a bit. It won't be
going into the next release, so there is no need to hurry up and do it for
your platform or translate the strings if you're a translator. It's just a
ColorSelector inside of a dialog.

I also cleaned up toggle-case functionality a bit, and used bools instead of
ints in pp_Property.cpp